The present invention relates to a respiration and heartbeat monitoring system employing a highly sensitive chest motion transducer and associated amplification and filter circuits. The invention is particularly well suited to the monitoring of respiration and heart rate in infants, although the invention may also be used in monitoring adults and animals.
Apnea or the transient cessation of respiration is a leading cause of death in infants. This malady is known to occur during sleep. Constant monitoring of the infant permits prompt detection of apnea and timely corrective action. Unfortunately, in infants normal respiration in sleep is characterized by extremely small chest movements. Detection of these movements and distinguishing them from heartbeat, associated vascular movements or muscle noise has proven difficult.
It is known in the prior art to measure respiration, and other body parameters characterized by mechanical movement, with piezoelectric transducers mechanically coupled to the body. Such systems are shown in U.S. Pat. No. 2,658,505 to Sheer, U.S. Pat. No. 3,782,368 to Reibold, and U.S. Pat. No. 4,185,621 to Morrow.
The Morrow and Sheer patents disclose mountings for piezoelectric crystals for measuring vascular blood flow parameters. The Reibold patent discloses a transducer for measuring respiration employing a large piezoelectric crystal of disc-like geometry bonded directly to a slightly larger metallic disc. Reibold attaches bending arms to the disc so that the arms extend outward from the chest. The arms secures them to ends of the discontinuous chest belt. The belt apparently couples chest expansion forces to the crystal and holds the discs adjacent the chest wall.
However, the Reibold device is not well suited to detection of small chest movements such as occur in respiration in infants.
Accordingly, it is an object of the present invention to provide a sensitive respiration transducer for monitoring respiration in infants.
It is another object of the present invention to provide sensitive respiration transducer employing a small, inexpensive piezoelectric crystal.
It is another object of the present invention to provide a respiration transducer which may be held against the chest of the subject by a relatively flat belt which overlies the transducer.
It is another object of the present invention to provide a sensitive respiration transducer for detecting chest wall flexure beneath the transducer.
Apnea may occur without immediate cessation of heartbeat or so-called "muscle noise" which is small muscle contractions or twitches not indicative of respiration. In such circumstances an extremely sensitive respiration transducer might produce erroneous indications of continued respiration due to detection of chest movements associated with heartbeat, vascular movements or muscle noise. In addition, such movements could distort normal respiration rates measured by such a sensitive transducer.
Accordingly, it is a further object of the present invention to provide a patient monitoring system employing a sensitive respiration transducer, which provides for the inhibiting of erroneous respiration indications caused by heartbeat, vascular movements and muscle noise.
These and other objects and features will be apparent from the written description, read with the associated drawings and claims.